Britain's reputation as a centre of aerospace excellence has received a setback, with work on a £13bn Ministry of Defence air tanker contract being transferred to Spain, putting 320 jobs at risk.

Cobham, a defence and aerospace industry supplier, said that work on converting Airbus A330 passenger planes into Voyager fuel tankers would be carried out near Madrid instead of Bournemouth. The move puts in doubt the jobs of 240 Cobham staff and 80 contractors, after the MoD said it could not have demanded that the work on the Voyager programme stayed in the UK.

The conversion is being carried out under a multibillion-pound private finance initiative run by the AirTanker consortium, whose members are EADS, the owner of Airbus; Cobham; Rolls-Royce; Babcock, the UK defence services group; and Thales of France.

Cobham said shifting the conversion of the final 10 aircraft to Madrid, where Airbus would carry out the work, would be more efficient because the design team behind the programme was based there.

"This will help to ensure the continued success of the programme by co-locating aircraft engineers undertaking the conversion with the Airbus design office in Spain, so greatly improving efficiency and shortening the supply chain," said Cobham, adding that the move would not have a material impact on its finances.

The decision evokes comparisons with the £1.4bn Thameslink trains contract, when the government chose Siemens of Germany as preferred bidder, over Britain's last remaining train factory in Derby. Value for money was a key factor in that decision and it is understood that under the terms of the Voyager contract the consortium will incur a financial charge if the conversions are carried out behind schedule.

Because the Airbus site in Getafe near Madrid has already proved adept at carrying out the work rapidly, the consortium decided to move the process to Spain. Cobham will seek to redeploy as many of the project's directly employed staff as possible, either to Spain or to the RAF Brize Norton air base in Oxfordshire to service the aircraft.

Voyager is a £13bn programme under which the consortium raises funds to pay for 14 fuel tankers and is reimbursed over the 24-year span of the contract, contingent on the consortium meeting deadlines.

An MoD spokesperson said: "We are disappointed by the decision by Cobham and Airbus Military to switch conversion of the Voyager aircraft to the Airbus military facility in Madrid, but understand why this commercial decision has been taken to ensure that AirTanker meets its contractual aircraft delivery schedule."

George Osborne singled out aerospace in the March budget as a key player in a drive to rebalance the economy, setting aside £60m for a centre of excellence in aerodynamics. The aerospace sector is one of the UK's strongest industrial pillars, employing 100,000 people and generating a turnover of £23bn. Shadow defence minister Alison Seabeck said: "Defence industrial decline, rather than reform to preserve our skills base, is coming to characterise this government. David Cameron can't just sit on the sidelines and watch high-skilled jobs like these disappear."

The air tankers are 60m (197ft) long and can carry 100,000 litres of fuel, which is used to refuel other planes at a rate of 5,000 litres a minute.

The Voyager contract has been criticised since it was announced in 2008, including claims that the planes lack the protective gear necessary to act in war zones. Earlier this year, AirTanker planes experienced leakage problems during in-flight test refuelling of British Tornado jets.